Direct shock tube measurements of oxygen-atom recombination rates

Abstract

Oxygen-atom recombination rates have been measured over the temperature range 3000 to 3800 K using a method which affords direct control over the recombination process stimulated in a rapidly expanded sample of gas in a shock tube. A knife edge ‘trap’ was placed in the shock tube channel in order to provide partial reflection of incident shock waves. Density variations in the expanded gas region were measured with a quantitative interferometric chronometer by using the helium-neon laser as a light source. Simultaneous pressure measurements enable the relaxation effect to be detected from a comparison of the local change of pressure with the density variations. A strong temperature dependence for the recombination rate coefficients with the oxygen molecule as the dominant catalyst was obtained in the limits (2·0 to 0·4) × 10 15 cm 6 mole −2 sec −1 at 3000 to 3800 K respectively. The data agree well with recombination rates evaluated from dissociation rate measurements. Some gas dynamic applications of the results to quasi-stationary expanded shock tube flow analysis are discussed. Measured decay distances of the recombination relaxation in rarefaction waves generated in non-equilibrium flows around a corner are in accordance with the recombination rate data.